Why Does My Child Need a TCD Ultrasound for Sickle Cell?

Your child needs an annual head ultrasound because children with sickle cell anemia (specifically the HbSS and HbSβ0 types) have a much higher risk of stroke. This painless test is the best way to spot that risk before a stroke happens ^[1][2]. The test, called a Transcranial Doppler (TCD), measures exactly how fast blood is moving through the major blood vessels in your child’s brain ^[3]. If the blood is moving too fast, it usually means the blood vessels are narrowed ^[4]. Catching this early is incredibly important because it allows doctors to start protective treatments—such as regular blood transfusions—which can stop a stroke from ever occurring ^[5].

What the Test is Like for Your Child

A TCD ultrasound uses sound waves to safely look at blood vessels inside the head, similar to the ultrasound used during pregnancy. It is completely non-invasive, does not use radiation, and doesn’t hurt ^[3].

During the appointment, the technician will place warm gel on your child’s head—typically around the temples or the back of the neck. Your child will just need to lie somewhat still while the technician glides a small wand over those areas. No sedation or medication is required, and many clinics encourage children to watch a favorite movie or play on a tablet to help them stay comfortable and distracted during the scan.

How It Finds Stroke Risk

In children with sickle cell anemia, sticky, sickle-shaped red blood cells can damage the inner lining of blood vessels. Over time, this damage can cause the arteries in the brain to become narrow, or stenosed ^[4]. Think of a garden hose: if you place your thumb over the opening to narrow it, the water shoots out much faster. In the same way, blood has to speed up to push through a narrowed artery ^[4]. By measuring this speed, the TCD tells doctors how narrowed the arteries might be.

Understanding the Results

When the technician performs the TCD, they are measuring the blood’s speed in centimeters per second (cm/s). The results typically fall into one of three categories:

• Normal: The blood flow is moving at a safe speed. However, because risk can change as your child grows, screening is strongly recommended every year from age 2 to 16 ^[1]. It is important to know that while a normal TCD is excellent news, it doesn’t catch every form of brain injury; some children may experience “silent” strokes (small areas of damage that do not cause obvious physical symptoms) ^[6]. Your care team manages this risk by watching for subtle signs (like learning struggles) and may recommend an MRI at specific ages to proactively check the brain’s health ^[7].
• Conditional (Borderline): Speeds are starting to increase (usually between 170 and 199 cm/s) but are not yet in the danger zone. Your doctor will likely want to repeat the TCD in a few months rather than waiting a full year to make sure the speeds aren’t climbing.
• Abnormal (High Risk): If the blood flow speed reaches 200 cm/s or higher, your child is at a very high risk for having a primary stroke ^[5].

If an abnormal result occurs, your medical team may also recommend an MRI to get a detailed look at the brain’s blood vessels to confirm what the TCD found ^[7].

Turning High Risk into Prevention

The main reason TCD screenings are an essential standard of care is that an “abnormal” result gives doctors a clear signal to intervene immediately.

If blood flow velocities are 200 cm/s or higher, the standard recommendation is to start prophylactic (preventative) chronic blood transfusion therapy ^[2]. This involves your child receiving healthy donor blood regularly. A landmark clinical trial showed that starting these regular transfusions reduces the risk of a first stroke by 92% in children with high TCD speeds ^[5]. Over time, these transfusions can even help lower the blood flow speeds back into the normal range ^[8].

If regular blood transfusions are not possible, a daily medication called hydroxyurea is an effective alternative strategy that can also lower TCD velocities and reduce stroke risk ^[9]. However, unlike the immediate protection of a transfusion, hydroxyurea takes time to reach its maximum protective effect, so your doctor will monitor your child closely while starting it.

While it is entirely normal to feel anxious about yearly tests, this screening is one of the most powerful tools available to protect your child’s developing brain.